Polycrystalline diamond and polycrystalline diamond-like elements are known, for the purposes of this specification, as PCD elements. PCD elements are formed from carbon based materials with exceptionally short inter-atomic distances between neighbouring atoms. One type of diamond-like material similar to PCD is known as carbonitride (CN) described in U.S. Pat. No. 5,776,615. In general, PCD elements are formed from a mix of materials processed under high-temperature and high-pressure into a polycrystalline matrix of inter-bonded superhard carbon based crystals. A common trait of PCD elements is the use of catalyzing materials during their formation, the residue from which often imposes a limit upon the maximum useful operating temperature of the element while in service.
A well known, manufactured form of PCD element is a two-layer or multi-layer PCD element where a facing table of polycrystalline diamond is integrally bonded to a substrate of less hard material, such as tungsten carbide. The PCD element may be in the form of a circular or part-circular tablet, or may be formed into other shapes. PCD elements of this type may be used in almost any application where a hard, wear- and erosion-resistant material is required. The substrate of the PCD element may be brazed to a carrier, often also of cemented tungsten carbide. This is a common configuration for PCDs used as cutting elements, for example in fixed cutter or rolling cutter earth boring bits when, received in a socket of the drill bit. These PCD elements are typically called polycrystalline diamond cutters (PDC).
Typically, higher diamond volume densities in the diamond table increases wear resistance at the expense of impact strength. However, modern PDCs typically utilize complex geometrical interfaces between the diamond table and the substrate as well as other physical design configurations to improve the impact strength. Although this allows wear resistance and impact strength to be simultaneously maximized, the trade-off still exists.
Another form of PCD element is a unitary PCD element without an integral substrate, where a table of polycrystalline diamond is fixed to a tool or wear surface by mechanical means or a bonding process. These PCD elements differ from those above in that diamond particles are present throughout the element. These PCD elements may be held in place mechanically, they may be embedded within a larger PCD element that has a substrate, or, alternately, they may be fabricated with a metallic layer which may be bonded by a brazing or welding process. A plurality of these PCD elements may be made from a single PCD, as shown, for example, in U.S. Pat. Nos. 4,481,016 and 4,525,179 herein incorporated by reference for all they disclose.
PCD elements are most often formed by sintering diamond powder with a suitable binder-catalyzing material in a high-pressure, high-temperature (HPHT) press. One particular method of forming polycrystalline diamond in this way is disclosed in U.S. Pat. No. 3,141,746 herein incorporated by reference for all it discloses. In one common process for manufacturing PCD elements, diamond powder is applied to the surface of a preformed tungsten carbide substrate incorporating cobalt. The assembly is then subjected to very high temperature and pressure in a press. During this process, cobalt migrates from the substrate into the diamond layer and acts as a binder-catalyzing material, causing the diamond particles to bond to one another with diamond-to-diamond bonding, and also causing the diamond layer to bond to the substrate.
The completed PCD element has at least one body with a matrix of diamond crystals bonded to each other with intercrystalline bonds and defining many interstices between the crystals which contain a binder-catalyzing material as described above. The diamond crystals comprise a first continuous matrix of diamond, and the interstices form a second continuous interstitial matrix of the binder-catalyzing material. In addition, there are necessarily a relatively few areas where the diamond to diamond growth has encapsulated some of the binder-catalyzing material. These ‘islands’ are not part of the continuous interstitial matrix of binder-catalyzing material.
Such PCD elements may be subject to thermal degradation due to differential thermal expansion between the interstitial cobalt binder-catalyzing material and the diamond matrix, beginning at temperatures of about 400 degrees C. Upon sufficient thermal expansion, the diamond-to-diamond bonding may be ruptured and cracks and chips may occur. The differential of thermal expansion may also be referred to as the differential of co-efficient of thermal expansion.
Also in polycrystalline diamond, the presence of the binder-catalyzing material in the interstitial regions adhering to the diamond crystals of the diamond matrix leads to another form of thermal degradation. Due to the presence of the binder-catalyzing material, the diamond is caused to graphitize as temperature increases, typically limiting the operation temperature to about 750 degrees C.
Although cobalt is most commonly used as the binder-catalyzing material, any group VIII element, including cobalt, nickel, iron, and alloys thereof, may be employed.
To reduce thermal degradation, so-called “thermally stable” polycrystalline diamond components have been produced as preform PCD elements for cutting- and/or wear-resistant elements, as disclosed in U.S. Pat. No. 4,224,380 herein incorporated by reference for all it discloses. In one type of thermally stable PCD element the cobalt or other binder-catalyzing material found in a conventional polycrystalline diamond element is leached out from the continuous interstitial matrix after formation. Numerous methods for leaching the binder-catalyzing material are known. Some leaching methods are disclosed, for example, in U.S. Pat. Nos. 4,572,722 and 4,797,241 both herein incorporated by reference for all they disclose.
Leaching the binder-catalyzing material may increase the temperature resistance of the diamond to about 1200 degrees C. However, the leaching process also has a tendency to remove the cemented carbide substrate. In addition, where there is no integral substrate or other bondable surface, there are severe difficulties in mounting such material for use in operation. There is some belief that it is advisable to not leach closer to the substrate than 500 microns.
The fabrication methods for such ‘thermally stable’ PCD elements typically produce relatively low diamond volume densities, typically of the order of 80 volume % or less. This low diamond volume density enables a thorough leaching process, but the resulting furnished part is typically relatively weak in impact strength. The low volume density is typically achieved by using an admixtures process and using relatively small diamond crystals with average particle sizes of about 15 microns or less. These small particles are typically coated with a catalyzing material prior to processing. The admixtures process causes the diamond particles to be widely spaced in the finished product and relatively small percentages of their outer surface areas dedicated to diamond-to-diamond bonding, often less than 50%, contributing to the low impact strengths.
In these so-called “thermally stable” polycrystalline diamond components, the lack of a suitable bondable substrate for later attachment to a work tool has been addressed by several methods. One such method to attach a bondable substrate to a “thermally stable” polycrystalline diamond preform is shown in U.S. Pat. No. 4,944,772 herein incorporated by reference for all it discloses. In this process, a porous polycrystalline diamond preform is first manufactured, and then it is re-sintered in the presence of a catalyzing material at high-temperatures and pressures with a barrier layer of another material which, in theory, prevents the catalyzing material from re-infiltrating the porous polycrystalline diamond preform. The resulting product typically has an abrupt transition between the preform and the barrier layer, causing problematic stress concentrations in service. This product is considered to be more like a joined composite than an integral body.
Other, similar processes to attach a bondable substrate to “thermally stable” polycrystalline diamond components are shown in U.S. Pat. Nos. 4,871,377 and 5,127,923 herein incorporated by reference for all they disclose. It is believed that the weakness of all these processes is the degradation of the diamond-to-diamond bonds in the polycrystalline diamond preform from the high temperature and pressure re-sintering process. It is felt that this degradation generally further reduces the impact strength of the finished product to an unacceptably low level below that of the preform.
In an alternative form of thermally stable polycrystalline diamond, silicon is used as the catalyzing material. The process for making polycrystalline diamond with a silicon catalyzing material is quite similar to that described above, except that, at synthesis temperatures and pressures, most of the silicon is reacted to form silicon carbide, which is not an effective catalyzing material. The thermal resistance is somewhat improved, but thermal degradation still occurs due to some residual silicon remaining, generally uniformly distributed in the interstices of the interstitial matrix. Again, there are mounting problems with this type of PCD element because there is no bondable surface.
More recently, a further type of PCD has become available in which carbonates, such as powdery carbonates of Mg, Ca, Sr, and Ba are used as the binder-catalyzing material when sintering the diamond powder. PCD of this type typically has greater wear-resistance and hardness than the previous types of PCD elements. However, the material is difficult to produce on a commercial scale since much higher pressures are required for sintering than is the case with conventional and thermally stable polycrystalline diamond. One result of this is that the bodies of polycrystalline diamond produced by this method are smaller than conventional polycrystalline diamond elements. Again, thermal degradation may still occur due to the residual binder-catalyzing material remaining in the interstices. Again, because there is no integral substrate or other bondable surface, there are difficulties in mounting this material to a working surface.
In some known techniques, physical vapor deposition (PVD) and/or chemical vapor deposition (CVD) processes are used to apply the diamond or diamond-like coating. PVD and CVD diamond coating processes are well known and are described, for example, in U.S. Pat. Nos. 5,439,492; 4,707,384; 4,645,977; 4,504,519; 4,486,286 all herein incorporated by reference.
PVD and/or CVD processes to coat surfaces with diamond or diamond like coatings may be used, for example, to provide a closely packed set of epitaxially oriented crystals of diamond or other superhard crystals on a surface. Although these materials have very high diamond densities because they are so closely packed, there is no significant amount of diamond to diamond bonding between adjacent crystals, making them quite weak overall, and subject to fracture when high shear loads are applied. The result is that although these coatings have very high diamond densities, they tend to be mechanically weak, causing very poor impact toughness and abrasion resistance when, used in highly loaded applications, such as when used as drill bit cutting elements.
Some attempts have been made to improve the toughness and wear resistance of these diamond or diamond-like coatings by applying them to a tungsten carbide substrate and subsequently processing them in a high-pressure, high-temperature environment, as described in U.S. Pat. Nos. 5,264,283; 5,496,638; 5,624,068, which are herein incorporated by reference for all they disclose. Although this type of processing may improve the wear resistance of the diamond layer, the abrupt transition between the high-density diamond layer and the substrate make the diamond layer susceptible to wholesale fracture at the interface at very low strains, similar to the above described problems encountered with composite structures having barrier layers. This again translates to very poor toughness and impact resistance in service.
U.S. Pat. No. 6,601,662 discloses PCD cutting elements which are adapted to control the wear profile of the cutting or working faces to increase the operating life of the cutting elements, primarily by making the elements self-sharpening so that a greater proportion of the cutter body can be worn away and used in effectively cutting material.
The cutting elements have one portion of the working surface which is treated to leach substantially all catalyst material from the interstices near the working surface of the PCD element in an acid etching process to a depth of greater than about 0.2 mm, in order to increase the wear resistance of the cutting elements. In particular, this provides a superhard polycrystalline diamond or diamond-like element with greatly improved wear resistance without loss of impact strength.
Each cutting element also has another surface which is not treated, such that some catalyzing material remains in the interstices, or, alternatively, the another surface is only partially treated, or at least less treated than the one portion of the working surface. In one embodiment, a gradual (continuous) change in the treatment is indicated. In this way, the treated, more wear-resistant portions cause the element to be self-sharpening.
Further disclosed arrangements include a treated surface and a surface which is not treated such that some catalyzing material remains in the interstices, and further include another surface which is only partially treated, or at least less treated than the treated surface.
Different arrangements of varied wear resistance on the front and side working surfaces of PCD cutting elements are also disclosed. Again, each has a treated surface and a surface which is not treated such that some catalyzing material remains in the interstices. The disclosed elements have two working surfaces (e.g. the PCD body end face and side wall) such that the varied wear resistance may be applied to either or both surfaces. Another surface which is only partially treated, or at least less treated than the treated surface, may also be included in place of portions of the untreated surface.
U.S. Pat. Nos. 5,517,589; 7,608,333; 7,740,673; and 7,754,333, and U.S. patent application Ser. Nos. 11/776,389 and 12/820,518, disclose various thermally stable diamond polycrystalline diamond constructions.
U.S. Pat. No. 5,120,327, issued to Diamant-Boart Stratabit (USA), Inc. and assigned to Halliburton Energy Services, Inc., discloses an carbide substrate and a diamond layer adhered to a surface of the substrate. That surface includes a plurality of spaced apart ridges forming grooves therebetween.